Ben Roling created CRUNCH-677:
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Summary: Support passing FileSystem to File Sources and Targets
Key: CRUNCH-677
URL: https://issues.apache.org/jira/browse/CRUNCH-677
Project: Crunch
Issue Type: Improvement
Components: Core
Reporter: Ben Roling
Assignee: Josh Wills
We'd like to pass a FileSystem instance to File Sources and Targets to fully
qualify the Path. Without the FileSystem, the Pipeline doesn't necessarily
have enough information to understand the Path. In particular, when the Path
is an HA HDFS path like "hdfs://my-cluster/data", the Pipeline itself may not
have the necessary
[configuration|https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/HDFSHighAvailabilityWithNFS.html#Configuration_details]
to resolve "hdfs://my-cluster".
While it is in some cases possible to seed the Pipeline configuration with all
the HDFS properties necessary to communicate with any HDFS HA cluster the
Pipeline might talk to, it can be awkward and/or difficult to do this in all
cases. We have cases where we'd like not to have to know all of the clusters
upfront.
With the proposed change, code like the following is possible, where
{{readFileSystem}} and {{writeFileSystem}} are external FileSystems synthesized
from Configuration completely separate from that used to construct the Pipeline
itself:
{code}
Configuration emptyConfiguration = new Configuration(false);
Pipeline pipeline = new MRPipeline(getClass(), emptyConfiguration);
FileSystem readFileSystem = ...;
PCollection<String> data =
pipeline.read(From.textFile("hdfs://my-cluster-1/data", readFileSystem));
FileSystem writeFileSystem = ...;
pipeline.write(data, To.textFile("hdfs://my-cluster-2/output",
writeFileSystem));
{code}
Note: the hdfs://my-cluster-1 and hdfs://my-cluster-2 parts of the paths would
not strictly need to be included as they would be implied by the FileSystem
instances passed in the calls. As such the paths could simply be passed as
"/data" and "/output" with equivalent behavior.
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